Polishing method

ABSTRACT

A polishing method is disclosed, which includes: conditioning a polishing pad, after polishing metal material of a previous wafer; spraying organic acid solution to the polishing pad; spraying deionized water to the polishing pad; performing a water-removing treatment on the polishing pad; and spraying polishing liquid to the polishing pad and polishing metal material of a next wafer. The method can prevent scratches on the surface of metal material of wafers and improve yield rate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the priority of Chinese Patent Application No. 201010603419.8, entitled “Polishing Method”, and filed on Dec. 23, 2010, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor manufacturing, and particularly relates to a polishing method.

2. Description of Prior Art

With the continuous development of the semiconductor manufacturing process, the critical dimension (CD) of semiconductor devices is getting smaller. Techniques of combining metal gate electrode and gate dielectric layer of High-K material are introduced into the manufacturing of the MOS transistor, to solve the problems caused by small critical dimension devices. Currently, High-K Metal Gate (HKMG) techniques have become the mainstream techniques for 32 nm technology and below, in which chemical mechanical polishing (CMP) on the metal gate electrode is one of the most important step. For the mechanism of CMP, it is described that: a surface layer which is relatively easy to remove is formed by reaction of the surface material of a wafer and polishing liquid, and the surface layer is then mechanically scraped off by polishing pressure and by relative motion between polishing pad and the wafer. Specifically, during the CMP of metal material, polishing liquid is in contact with the surface of the metal material, and metal oxide is generated which is then mechanically scraped off to achieve the effect of polishing.

The most popular material for metal gate electrode is aluminum and Cu—Al alloy (in which aluminum is the major component). Large part of the by-product (i.e. metal oxide, which is mainly alumina and aluminum hydroxide) of the CMP on aluminum is left in the trench of the polishing pad. However, since aluminum has a very low hardness compared with the by-product of the CMP, during the CMP processes on aluminum of follow-up wafers, the surface of the aluminum will be scratched, which affects the functionality and reliability of semiconductor devices. Also the by-product is not dissolved in deionized water; therefore, it is difficult to be totally cleaned by conventional methods (such as spraying deionized water).

SUMMARY OF THE INVENTION

The present invention is to solve the problem that during the polishing process on metal material of a wafer, by-product left on the polishing pad scratches the surface of the metal material which has a very low hardness compared with the by-product.

To solve the above problem, there is provided a polishing method in the present invention, which includes:

conditioning a polishing pad, after polishing metal material of a previous wafer;

spraying organic acid solution to the polishing pad;

spraying deionized water to the polishing pad;

performing a water-removing treatment on the polishing pad;

spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.

Optionally, the conditioning of the polishing pad is pad ex-situ condition.

Optionally, the spraying organic acid solution to the polishing pad has a flow rate of 100˜1000 ml/min.

Optionally, during the spraying organic acid solution to the polishing pad, a platen has a rotation speed of 10˜150 RPM (Revolutions per Minute).

Optionally, the spraying deionized water to the polishing pad has a flow rate of 100˜1000 ml/min.

Optionally, during the spraying deionized water to the polishing pad, a platen has a rotation speed of 10˜120 RPM.

Optionally, the spraying polishing liquid to the polishing pad includes: polishing liquid covering the entire polishing pad.

Optionally, the spraying polishing liquid to the polishing pad has a flow rate of 100˜1500 ml/min and a spraying time of 5˜100 seconds.

Optionally, the organic acid is oxalic acid, malonic acid, succinic acid, maleic acid, phthalic acid or amino acid.

Optionally, the organic acid solution has a concentration of 0.01˜10 wt %.

Optionally, the metal material is aluminum or aluminum alloy.

In comparison with the conventional technology, the present invention has the following advantages:

By-product, which is generated during the polishing on a previous wafer and is left on the polishing pad, will be dragged out of the trench of the polishing pad during brushing of the polishing pad. In addition, the by-product is dissolved in the organic acid; the dissolved by-product and the organic acid are then removed by spraying deionized water, which effectively removes the by-product left in trenches of the polishing pad and prevents the by-product from scratching the surface of the metal material of a next wafer.

After performing a water-removing treatment on the polishing pad, the spraying polishing liquid to the polishing pad makes the polishing liquid cover the whole polishing pad, which further avoids scratching to the surface of the metal material and improves the yield rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of the polishing method in one embodiment of the present invention;

FIG. 2 to FIG. 6 are schematic views of steps in the polishing method in another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereunder, the present invention will be described in detail with reference to embodiments, in conjunction with the accompanying drawings.

Embodiments to which the present invention is applied are described, in detail below. However, the invention is not restricted to the embodiments described below.

As discussed in the background, in a conventional polishing process, by-product of CMP of aluminum (i.e. metal oxide generated in oxidation of aluminum by polishing agent, which is mainly alumina and aluminum hydroxide) will be left in trenches of the polishing pad. Since aluminum has a very low hardness compared with the by-product, for example the hardness of aluminum is 160 Mpa while the hardness of aluminum hydroxide is 20000 Mpa, the by-product which is left in the trenches of the polishing pad will scratches the surface of the aluminum during the CMP of a next wafer. The by-product which is left in trenches of the polishing pad can not be found by naked eyes, and is all over the trenches of the polishing pad under a scanning electron microscope (SEM). It is found that the scratches of different sizes on the surface of the metal material are generated by the left by-product. If the metal gate electrode is scratched, the functionality and reliability of semiconductor devices will be affected. Since the by-product is not dissolved in deionized water, it can not be cleaned well even with large amount of deionized water.

To prevent by-product from scratching the surface of the metal material, there is provided a polishing method in an embodiment of the present invention.

FIG. 1 is a flow diagram of the polishing method in this embodiment, which includes:

S101, conditioning a polishing pad, after polishing metal material of a previous wafer;

S102, spraying organic acid solution to the polishing pad;

S103, spraying deionized water to the polishing pad;

S104, performing a water-removing treatment on the polishing pad; and

S105, spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.

The polishing method will be described in detail with reference to another embodiment, in conjunction with FIG. 1 and FIG. 2 to FIG. 6.

FIG. 2 illustrates the principle of a polishing apparatus. As shown in FIG. 2, the polishing apparatus mainly includes a platen 101, a polishing head (grinding head) 103, a polishing pad 102 positioned over the platen 101, and a polishing liquid nozzle 104. Before polishing, a wafer 100 is placed in the polishing apparatus. Specifically in this embodiment, take polishing Al for example, the polishing liquid nozzle 104 sprays polishing liquid 105 that contains polishing agent to the polishing pad 102; the wafer 100, which is affixed to the polishing head by vacuum suction, is placed in the polishing liquid 105 on the polishing pad 102. The polishing agent oxidizes the surface of the metal on the wafer 100 into metal oxide (mainly alumina and aluminum hydroxide); the polishing head 103 imposes downward pressure; the platen 101 rotates with the polishing pad 102 (the polishing head can rotate in an opposite direction); the metal oxide on the surface of the wafer 100 is then mechanically scraped off by pressure and by relative motion between polishing pad 102 and the wafer. In addition, during the polishing process, the polishing head 103 can move back and forth in the horizontal direction with the wafer 100.

As discussed above, the metal oxide is the by-product during the polishing of Al, and a large part of the by-product is left in the trenches of the polishing pad 102. If not cleaned well, the by-product in the trenches will scratch the surface of the Al of a next wafer during polishing, which will affect the device performance.

Referring to FIG. 1 and FIG. 3, in step S101, when the polishing of metal material of a previous wafer is finished, the polishing pad is conditioned. For a better conditioning result, in this embodiment, the condition to the polishing pad 102 is a pad ex-situ condition, which is conditioning the polishing pad 102 between wafer polishing cycles. Specifically, after the metal material Al of the previous wafer is polished, the wafer is moved off the polishing pad 102 (the platen 101 stops rotating before moving the wafer off the polishing pad 102). The polishing pad 102 is then washed by deionized water and is scrubbed by the pad conditioner 106, which achieves the condition of the polishing pad 102. Since a large part of the by-product is left in the trenches of the polishing pad 102, which can not be cleaned completely only by spraying deionized water, pad conditioner 106 is used to drag the by-product out of the trenches of the polishing pad 102, for the following cleaning steps. In other embodiments of the present invention, the polishing pad 102 can be conditioned by pad in-situ condition, which is to condition the polishing pad during a wafer polishing cycle. Specifically, during the polishing cycle of the previous wafer, the polishing pad 102 is scrubbed by the pad conditioner 106.

Referring to FIG. 1 and FIG. 4, step 102 is performed as: spraying organic acid solution to the polishing pad. Specifically, the spraying of organic acid solution to the polishing pad 102 has a flow rate of 100˜1000 ml/min. Meanwhile, the platen 101 is started (rotating); and the platen has a rotation speed of 10˜150 RPM. The platen 101 rotates in a middle or low rotation speed and the organic acid is sprayed with a high speed, which makes the by-product (alumina, aluminum hydroxide, etc.) dragged out by the pad conditioner 106 in S101 fully dissolved in the organic acid. The organic acid can be oxalic acid, malonic acid, succinic acid, maleic acid, phthalic acid or amino acid. The concentration of the organic acid solution is 0.01˜10 wt % (weight %).

Still referring to FIG. 1 and FIG. 4, step S103 is performed as: spraying deionized water to the polishing pad. Specifically, spraying deionized water to the polishing pad has a flow rate of 100˜1000 ml/min; meanwhile, the platen 101 is rotating and has a rotation speed of 10˜120 RPM. The platen 101 rotates in a low speed and the deionized water is sprayed with a high speed, which removes the organic acid and the by-product dissolved in the organic acid in S102.

Referring to FIG. 1 and FIG. 5, step S104 is performed as: performing a water-removing treatment on the polishing pad. Specifically, the water-removing treatment is performed in a conventional way, in which the platen 101 rotates in high speed to remove the deionized water on the polishing pad 102. During the rotation of the platen 101, desiccant can be used on the polishing pad 102 for a drying process; the desiccant is nitrogen.

Referring to FIG. 1 and FIG. 6, step S105 is performed as: spraying polishing liquid to the polishing pad and polishing metal material of a next wafer. Specifically, the polishing liquid 105 is sprayed through polishing liquid nozzle 104 to the polishing pad 102, and covers the entire polishing pad 102 (the polishing liquid 105 shown in FIG. 6 has not covered the entire polishing pad yet). During the spraying of the polishing liquid, the spraying has a flow rate of 100˜1500 ml/min and a spraying time of 5˜100 seconds, to make the polishing liquid 105 cover the whole polishing pad 102. In this way, before polishing metal material of a next wafer, the polishing pad 102 is covered with polishing liquid 105 that is used for polishing aluminum, which can ensure full contact between the polishing liquid 105 and the aluminum. The aluminum will be oxidized by the polishing agent in polishing liquid 105, which can further protect the surface of the aluminum from the left by-product after the steps from S101 to S104 and further improves the yield rate. In other embodiments, the polishing a next wafer and the spraying polishing liquid can be performed at the same time.

In the above embodiments, the metal material is aluminum or aluminum alloy. In other embodiments of the present invention, the polishing method provided can also apply to polishing process in which metal material has a low hardness.

In comparison with the conventional technology, the present invention has the following advantages:

By-product, which is generated during the polishing on a previous wafer and is left on the polishing pad, will be dragged out of the trench of the polishing pad during brushing of the polishing pad. In addition, the by-product is dissolved in the organic acid; the dissolved by-product and the organic acid are then removed by spraying deionized water, which effectively removes the by-product left in trenches of the polishing pad and prevents the by-product from scratching the surface of the metal material of a next wafer.

After performing a water-removing treatment on the polishing pad, the spraying polishing liquid to the polishing pad makes the polishing liquid cover the whole polishing pad, which further avoids scratching to the surface of the metal material and improves the yield rate.

Although the present invention has been illustrated and described with reference to the preferred embodiments of the present invention, those ordinary skilled in the art shall appreciate that various modifications in form and detail may be made without departing from the spirit and scope of the invention. 

1. A polishing method, comprising: conditioning a polishing pad, after polishing metal material of a previous wafer; spraying organic acid solution to the polishing pad; spraying deionized water to the polishing pad; performing a water-removing treatment on the polishing pad; and spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.
 2. The polishing method of claim 1, wherein the conditioning of the polishing pad is pad ex-situ condition.
 3. The polishing method of claim 1, wherein the spraying organic acid solution to the polishing pad has a flow rate of 100˜1000 ml/min.
 4. The polishing method of claim 3, wherein during the spraying organic acid solution to the polishing pad, a platen has a rotation speed of 10˜150 RPM.
 5. The polishing method of claim 1, wherein the spraying deionized water to the polishing pad has a flow rate of 100˜1000 ml/min.
 6. The polishing method of claim 5, wherein during the spraying deionized water to the polishing pad, a platen has a rotation speed of 10˜120 RPM.
 7. The polishing method of claim 1, wherein the spraying polishing liquid to the polishing pad includes: polishing liquid covering the entire polishing pad.
 8. The polishing method of claim 7, wherein the spraying polishing liquid to the polishing pad has a flow rate of 100˜1500 ml/min and a spraying time of 5˜100 seconds.
 9. The polishing method of claim 1, wherein the organic acid is oxalic acid, malonic acid, succinic acid, maleic acid, phthalic acid or amino acid.
 10. The polishing method of claim 1, wherein the organic acid solution has a concentration of 0.01˜10 wt %.
 11. The polishing method of claim 1, wherein the metal material is aluminum or aluminum alloy. 